Conventional communication system switches, such as private branch exchanges (PBXs) and other premises-based telephone switches, generally support a wide variety of useful features, such as bridged call appearances, hunt groups, call forwarding, navigable directories, multi-call conferencing, etc.
However, these and other switch-based features are typically provided only to those user terminals that represent internal extensions within the premises serviced by the switch. As a result, a user terminal associated with an external network is generally unable to avail itself of the full set of features supported by the switch.
By way of example, a mobile telephone or other mobile device representing a given external endpoint of the system generally cannot be treated as an internal extension of a conventional switch. A call directed from an internal extension of the switch to the given endpoint therefore must be processed as any other call to an endpoint of an external network, even if the given external endpoint is a device known to be associated with a user of an internal extension of the switch.
It is known in the art to implement call forwarding routines that will allow a call directed from one internal extension to another to be forwarded to a designated mobile telephone or other endpoint of an external network. However, in conventional call forwarding, the designated mobile telephone is not treated as if it were an internal extension serviced by the switch, and is generally unable to access many desirable features of the switch. Conventional switches are thus typically unable to extend switch-based features to such a call in an efficient and cost-effective manner.
Techniques for addressing this problem are described in U.S. patent application Ser. No. 09/908,155 entitled “Method and Apparatus for Treating Externally-Originated Calls as Coming from Internal Switch Extensions,” and U.S. patent application Ser. No. 09/908,156 entitled “Method and Apparatus for Extending Calls to Internal Switch Extensions out to External Network Endpoints,” both filed Jul. 18, 2001 in the name of inventor Stephen M. Milton, commonly assigned herewith and incorporated by reference herein. Advantageously, these techniques allow mobile telephones and other external system endpoints to access premises-based communication switch features in a manner similar to an internal extension serviced by the switch.
As described in the above-cited U.S. patent application Ser. No. 09/908,156, it is possible for a single external endpoint, such as an endpoint referred to therein as an “Xmobile” endpoint, to support simultaneously multiple calls each associated with a different trunk. As a more particular example, it is possible for the switch to be configured such that two calls may be directed to a given registered external endpoint using two different trunks, each associated with a different external port of the switch. However, such an arrangement generally utilizes the two different trunks even under a conference or transfer condition in which an external voice connection is established between the two trunk calls in an external network, e.g., an external wireless cellular network.
Therefore, despite the considerable advantages provided by the techniques described the above-cited applications, a need remains for further improvements in switch-based call processing, particularly with regard to the handling of multiple trunks associated with calls supported by a single external endpoint.